The present invention relates to a printing apparatus such as a printer or a plotter, and more particularly to the optimization of a method for transferring data to a print head having a shift register installed therein.
Normally, a printing apparatus, such as an ink jet printer or plotter, repeats printing and paper sheet feeding to complete an image while moving the print head across the paper sheet.
To send print data to the print head carried on the carriage, the data is sent from a central processor (engine controller), which controls the printing apparatus, to the print head via a cable.
With the introduction of a full-color, high-speed printing apparatus, more heads are installed in the apparatus, usually four and, in some cases, six. This requires more signal lines between the central processor and the carriage, increasing both the apparatus size and the cost.
In addition, because of the use of a flexible flat cable, more signal lines not only increase the cost but make the radiation noise problem more serious. Therefore, there is a need for minimizing the number of signal lines.
FIGS. 17 and 18 show examples of a conventional method for connection between the engine controller and the carriage. In the conventional method shown in FIG. 17, the largest number of signal lines is used because all data for each head are transferred independently to each print head.
On the other hand, in a conventional method shown in FIG. 18, head data (HDDATA) and drive signals (HDDRIVE) are sent independently to each head while a data transfer clock (HDCLK) and a latch clock (HDLTCLK) are shared by the heads. This configuration uses less signal lines than the configuration shown in FIG. 17. However, as shown in the timing chart in FIG. 19, 128 bits of data are continuously sent to one head and 128 bits of data are latched at the same time in the configuration shown in FIG. 18. In this configuration, data is transferred to each head, one slice at a time and, therefore, fine print timing adjustment cannot be made. (In this specification, a xe2x80x9cslicexe2x80x9d represents a group of pixels of the number of one-horizontal-pixel by vertical print nozzles (128 pixels in this case), as one unit. A slice corresponds to a time slot required to transfer a unit of print data corresponding to a plurality of print nozzles on a plurality of heads). Thus, when printing data in color, color mixture adjustment is made by one dot. Because human eye can normally identify a color difference of up to 1/4 pixel, it is known that adjustment of 1/4 pixel or less is needed to avoid a problem.
Therefore, it is an object of the present invention to provide a print data transfer method and printing apparatus that reduce the number of signal lines used in the cable between the printing apparatus controller and the carriage and that can adjust the print timing of each head by less than one pixel.
The print data transfer method according to the present invention is a method for transferring print data from a controller to a carriage via a cable for use in a printing apparatus which performs printing while moving the carriage bi-directionally over a sheet of paper, the carriage carrying thereon a plurality of print heads each having a plurality of dot printing elements, wherein the cable comprises a signal line via which serial print data to be supplied to the plurality of print heads is transferred in a predetermined order, a signal line via which a clock signal corresponding to individual bits of the serial print data is transferred, signal lines via which a signal indicating which print head corresponds to which print data included in the serial print data is transferred, and signal lines via which drive signals of the heads are transferred, the method comprising the steps of dividing one slice section into a plurality of sections, the slice section corresponding to a time slot required to transfer a unit of print data corresponding to the plurality of dot printing elements of the plurality of heads and further dividing each divided section into a number of subsections, the number being equal to the number of the print heads; assigning the different subsections of each divided section to the plurality of print heads; dividing the unit of print data for each print head into the number of the plurality of divided sections; and starting a transfer of the print data of each print head independently of the print data of other print heads, beginning with any one of the plurality of subsections assigned to that particular print head in one slice section.
According to the present invention, because print data for the plurality of print heads is converted to serial data for transfer over the cable, the number of signals in the cable can be reduced. At the same time, one slice section is divided into a plurality of sections, each of these divided sections is further divided into a number of subsections, the number being equal to the number of the print heads, and the different subsections of each divided section are assigned to the plurality of print heads. This enables the print timing of each print head to be adjusted in increments of less than one pixel. As a result, this minimizes color misalignment in color printing and ruled-line misalignment caused by misalignment of the heads.
In the above printing apparatus, for example, four print heads are used as the plurality of print heads, the one slice section is divided at least into four divided sections, and each divided section is further divided into four subsections.
The apparatus for implementing the method according to the present invention is a printing apparatus which performs printing while moving a carriage bi-directionally over a sheet of paper, the carriage carrying thereon a plurality of print heads each having a plurality of dot printing elements, the printing apparatus comprising a controller for generating serial print data including print data for the plurality of print heads in a predetermined order, a clock signal corresponding to individual bits of the serial print data, a signal indicating which print head corresponds to which print data included in the serial print data, and a drive signal of each head; a cable for transferring the serial print data and various signals generated by the controller to the carriage; and a signal distributing means for distributing the print data and the various signals received from the cable to the plurality of print heads, wherein the controller divides one slice section into a plurality of sections, the slice corresponding to a time slot required to transfer a unit of print data corresponding to the plurality of dot printing elements of the plurality of heads; further divides each divided section into a number of subsections, the number being equal to the number of the print heads; assigns the different subsections of each divided section to the plurality of print heads; divides the unit of print data for each print head into the number of the plurality of divided sections; and starts a transfer of the print data of each print head independently of the print data of other print heads, beginning with a specified subsection of the plurality of subsections assigned to that particular print head in the divided section.
More specifically, each print head has a plurality of dot print means arranged in a direction substantially perpendicular to a carriage moving direction and the print data for the plurality of dot print means of one print head is transferred using the plurality of subsections assigned to that particular print head.